Background There is minimal published data on outcomes of patients presenting with ST elevation myocardial infarction (STEMI) due to an ectatic infarct-related artery (EIRA). The aim of this study was to analyse the clinical characteristics and outcomes of these patients presenting for primary percutaneous coronary intervention (P-PCI) in comparison with non-EIRA. Methods Of the 1834 patients who presented at our institution for P-PCI between February 2008 and November 2013, 25 (1.4%) were identified as having an EIRA. These patients were compared with those with non-EIRA (80 patients) who were age, gender and lesion matched. Further sub-group analysis on in-hospital and long-term outcomes was done comparing EIRA stented and non-stented patients. Clinical events evaluated include death, recurrent infarction, unstable angina, or target lesion revascularisation (TLR). Results Baseline characteristics were similar between patients with EIRA and non-EIRA although none of those with EIRA had diabetes mellitus. By comparison to the non-EIRA group, the major procedural differences for patients with EIRA were (1) a greater incidence of large thrombus burden (96.0% vs 22.5%, p = 0.0001), (2) increased usage of peri-procedural glycoprotein IIb/IIIa inhibitors (72.0% vs 37.5%, p = 0.01) and post-procedural anticoagulation (28.0% vs 5.0%, p = 0.004), (3) larger mean stent dimension (3.9 ± 0.8 mm vs 3.4 ± 0.6 mm, p = 0.04) and (4) a higher percentage of P-PCI cases that did not have stent deployment (44.0% vs 7.5%, p = 0.0001). Patients with STEMI from EIRA had similar in-hospital outcomes but a higher long-term incidence of composite cardiovascular events at mean follow-up of 36.6 ± 14.1 months (44.0% vs 16.3% for non-EIRA, p = 0.01). Although patients with EIRA who received stenting had better in-hospital outcomes than the non-stented cohort (composite cardiovascular event rate: 0.0% vs 36.4%, p = 0.03), long-term outcomes were comparable (35.7% vs 54.6%, p = 0.59) due to a relatively high frequency of non-fatal MI and unstable angina in both groups. Conclusion Patients with STEMI due to EIRA carry worse long-term outcomes than those with non-EIRA. While successful stent deployment in the setting of EIRA improves procedural and inpatient success rates, it does not necessarily convey benefit to long-term event rates due to recurrent acute coronary syndromes.